A thin plating film attached to a plating surface (referred to as a front surface) of a wafer is formed by use of an electroplating apparatus. In the electroplating apparatus, a conductive base film is disposed on a front side on which a plating film is being formed and, with the base film as a cathode, a current is flowed in a plating solution to precipitate a plating film on the base film.
As an existing electroplating apparatus, an apparatus where the plating is carried out with a front side of a wafer turned downward (referred to as a bottom surface plating method) and an apparatus where the plating is carried out with the front side turned upward (referred to as a top surface plating method) are in use.
In the electroplating apparatus for bottom surface plating method, an anode electrode is disposed at a bottom portion of a plating bath, on an upper side thereof a wafer holder is disposed movable up and down, on the wafer holder a wafer is placed with a front side turned downward, after that a cathode holder is inserted in the wafer holder, a spring contact type cathode electrode is brought into contact with a back side of the wafer under pressure and the wafer is energized.
In the bottom surface plating method, since a wafer and a wafer holder are manually set to carry out the plating with a front side turned downward, the operating efficiency is not good. In this connection, in order to improve the operating efficiency, an automation apparatus is considered.
However, the process of setting a cathode electrode and a wafer can be automated only in a very complicated manner. In a Permalloy plating apparatus where the plating is applied with a magnetic field applied to give the directionality, the automation in the bottom surface plating method is difficult and has not yet been put into practical use.
Furthermore, in the plating apparatus for the top surface plating method, an anode electrode is disposed on an upper portion of a plating bath, at a bottom portion thereof a cathode holder having an engaging hole is disposed, a wafer holder is disposed detachably with the engaging hole and a wafer is placed on the wafer holder with a front side thereof turned upward. After that, an electrode housing recess of the wafer holder, in which a spring contact type cathode electrode is accommodated is evacuated to hold the wafer, the electrode is brought into contact with a backside of the wafer and the wafer holder is lifted and inserted into the engaging hole to closely seal the bottom portion.
The above-described top surface plating apparatus has problems outlined below.
That is, in order to automate an electroplating apparatus, when a wafer is placed on a wafer holder, the wafer has to be assuredly held and a cathode electrode has to be brought into contact with a backside of the wafer at a predetermined contact pressure to enable an assured energization.
However, a tip end of the cathode electrode, in consideration of a bending portion, is disposed a little above a top surface of the wafer holder and the cathode electrode applies pressure in a direction in which the wafer is detached from the wafer holder; accordingly, the wafer cannot be brought into contact with a top surface of the wafer holder. As a result, when a vacuum line is operated, the electrode recess cannot be evacuated, the wafer holder cannot assuredly hold the wafer and desired contact pressure of the cathode electrode can be obtained only with great difficulty.
In order to overcome the above-mentioned problems, what is mentioned below can be considered.
In an electrode housing recess of a wafer holder, a lift unit is disposed to displace a cathode electrode. When a wafer is placed on the wafer holder, the cathode electrode is moved downward so that a tip end thereof may not protrude from a top surface of the wafer holder, after the wafer holder on which the wafer has been placed is inserted in an engaging hole, the lift unit is driven to lift the cathode electrode to bring the tip end thereof into contact under pressure with a backside of the wafer.
However, according to the method, the lift apparatus has to be disposed inside of a small wafer holder; accordingly, the apparatus becomes very complicated and is difficult to put into practical use.